1. Field of the Invention
The present invention relates to a control unit of an automatic transmission which provides speed reduction control with good responsiveness to a speed reduction demand by a driver of the vehicle.
2. Description of Related Art
Speed reduction responsive to a speed reduction operation by a driver of a vehicle, such as a sudden release of the accelerator, braking or the like, is conventionally provided by a control system which monitors reduction in vehicle speed during brake operation, performs a down-shift operation when it is judged that the reduction in speed has reached a predetermined large value, and effects speed reduction by engine braking. However, with this conventional control system, there is a time delay between depression of the brake and the reduction in speed reaching the predetermined large value, and a down-shift operation cannot be performed during that time delay. Accordingly, an undesirably long time delay occurs before engine braking is actually provided by a down-shift operation after the driver demands the speed reduction, i.e., the system does not provide good responsiveness.
Further, since the speed change operation is generally performed based on a speed change map, an up-shift operation is performed responsive to an accelerator OFF operation. There are times when a down-shift operation may be performed due to the reduction in speed becoming equal to or greater than a predetermined value. In this case, the up-shift operation and the down-shift operation are both performed within a short time interval, thereby causing discomfort to the driver.